Plasma polymerization of allyl alcohol on polyolefin-based materials: characterization and adhesion properties

Hydroxyl-rich surfaces have been obtained through the plasma polymerization of allyl alcohol on various polyolefin-based substrates. The influence of plasma parameters (deposition time and power), the type of substrate, and water washing on the chemical structure of the formed plasma polymers was investigated. The characterization involved contact angle measurements, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) analyses. To increase the sensitivity of XPS towards hydroxyl groups, derivatization with trifluoroacetic anhydride was performed. In addition, the adhesion between plasma-polymerized layers and a two-component polyurethane lacquer was evaluated by a 90° peel test. It was shown that power had a pronounced influence on both water wettability and hydroxyl group retention, while deposition time mainly influenced the film thickness. A relationship between the extent of hydroxyl functionality and the loss of material during the washing procedure was also found. Furthermore, it was shown that the chemical structure of the plasma polymers was not seriously affected by the choice of substrate. On the contrary, the adhesion properties of the substrates with plasma-polymerized layers were found to be highly dependent on the substrate used. For one of the substrates, the adhesion tests revealed an excellent lacquer adhesion when appropriate process parameters during the plasma deposition were used. The other substrate showed considerably lower peel forces. The difference in adhesion properties between the substrates may be explained as an effect of vacuum-ultraviolet (VUV) emission present during the plasma deposition. The VUV emission is able to create radicals in the near-surface region of the substrate and thereby cause chain scission reactions, lowering the cohesive strength of the substrate. Finally, this study showed that reflection absorption spectroscopy (RAS) is a suitable FTIR technique for obtaining structural information about plasma-polymerized layers thinner than 50 nm.     

Improving the adhesion properties of polypropylene using a liquid-phase sulfonation treatment

This work describes the effects of a stable, short-reaction time, liquid-phase sulfonation technique aimed at improving the adhesion properties of polypropylene. The relationships among SO₃ concentration (0.15, 0.2, and 0.3 N), treatment time, surface chemistry, and adhesion debond strength have been investigated for polypropylene (PP) sheets sulfonated with SO₃ dissolved in 1,1,2-trichloro 1,2,2-trifluoroethane and neutralized using ammonium hydroxide (NH₄OH) or polyethyleneimine (PEI). It was confirmed that PEI neutralized specimens, compared to untreated PP, exhibited a larger increase in debond strength (~269% increase) than similarly treated specimens neutralized with NH₄OH (~210% increase). ATR-FTIR spectroscopy indicates the formation of sulfonic acid, ethylenic, ketone and alcoholic hydroxyl groups. These results are supported by X-ray photoelectron spectroscopy (XPS) that show the O : C ratios increasing from 0.03 to 0.25 for both the NH₄OH and PEI, and the S : C atomic ratios increasing from 0.0 to 0.05 and 0.06 for the NH₄OH and PEI, respectively. Furthermore, XPS examination of PEI neutralized specimens revealed a nitrogenated surface (~6%), providing evidence that PEI had grafted onto the sulfonated surface. The observed increases in adhesion are attributed to formation of polar functionalities and increased wettability (as measured by water contact angle measurements). The neutralizing agent also affects degree of adhesion improvement: the PEI causes larger increases in adhesion compared to the NH₄OH. The physical effects of sulfonation were examined using environmental scanning electron microscopy (ESEM), which showed crack formation after 2 min of treatment. Sulfonation times beyond 5 min degraded the polymer surface (severe microcracking and sloughing of the surface layer) decreasing the adhesion debond strength.     

Effects of environment and heat treatment on an oxygen plasma-treated polyimide surface and its adhesion to a chromium overcoat

—The effects of oxygen plasma treatment time, duration of storage, and heat treatment on the surface chemistry of and Cr adhesion to Dupont RC5878 and Kapton polyimides were investigated using X-ray photoelectron spectroscopy (XPS), and contact angle and peel strength measurements. The XPS results indicate that the initial stage of plasma treatment involves oxygen adsorption with insignificant modification of the surface chemistry. After 5 s of plasma treatment the surface chemistry is modified, as suggested by the changes in the carbonyl and partially oxidized carbon functional groups' contributions to the C(1s) line shape. These modifications resulted in an increase in the peel strength and a decrease in the contact angle of water. Over the first month of storage, the intensity of the carbonyl functional group peak decreased, while the contact angle increased and reached a steady-state value of 30° after 20 days of storage. These changes are mainly attributed to moisture absorption. Importantly, the metal adhesion to polyimide remained fairly constant over the storage period. The aged plasma-treated surface experienced loss of moisture when baked at 150°C for less than 5 min. This was followed by an increase of the partially oxidized carbon at the expense of the plasma-induced carbon-oxygen bonds at higher baking temperatures or longer times.     

Affect of adhesion and properties of kenaf (Hibiscus cannabinus L.) stem in particleboard performance

The objective of this work was to evaluate the adhesion and basic properties of kenaf stem, and its physical and mechanical properties on particleboard panels. In this study, rubberwood (RW) was used as a control. Single-layer experimental panels were produced from whole stem, core, and bast particles of kenaf. Findings revealed that the core part resulted in higher wettability and lower contact angle than the bast. Kenaf bast (KB) gave the highest buffering capacity, while kenaf core (KC) gave the lowest buffering capacity towards acid. The lowest specific gravity was shown by KC followed by kenaf whole stem (KWS) and KB. For particle analysis, KWS gave the highest acceptable particle distribution (73.9%), whilst KC, KB, and RW had particle distributions of 62.5, 68.1, and 56.8%, respectively. Particleboard panels produced from KWS had the highest average values of modulus of rupture and modulus of elasticity with good compaction under scanning electron microscopic. Panels made from bast particles had the lowest mechanical properties among the three types of panels. The internal bonding strengths and dimensional stability of the specimens followed the similar trend above. The results of this study indicate that the specific gravity and adhesion properties of the starting material play a role in determining the physical and mechanical properties of the particleboard panels.     

Adhesion characteristics of plasma-treated polypropylene to mild steel

The ability of polypropylene (PP) to adhere to mild steel depends to a large extent on the surface characteristics of both PP and steel. The adhesion of PP was improved by treatment in a cold plasma from oxidizing gases (O₂, H₂O, etc.). This surface functionalization was followed ex situ by means of contact angle measurements and XPS (X-ray photelectron spectroscopy) analysis. The polymer/steel assembly was fabricated by hot-pressing in vacuum, or after exposure to ambient air. Adhesion to steel, as determined by the lap-shear test, increased when the PP was treated with Ar-containing plasma gas and joined to steel after exposure to room atmosphere. Correlations between the polarity, the atomic (O/C, N/C) ratio, the dispersive component of the surface energy, and the degree of PP/steel adhesion are discussed.     

Wettability and adhesion studies of plasma-treated plastic substrates for gelatin holograms

The feasibility study of using polycarbonate and poly(methyl methacrylate) substrates treated with the oxygen plasma for dichromated gelatin holograms is reported. The contact angles of water on both treated and untreated substrates were measured to indicate the wettability of substrate surfaces. An appreciable increase in adhesion between the dichromated gelatin film and the polycarbonate substrate after the oxygen plasma treatment was demonstrated.     

Wetting and adhesion of water-borne printing inks on surface-modified polyolefins

Polyolefin films were surface-modified by different methods to improve the wetting and adhesion of water-borne printing inks. Polyethylene (PE) films were treated with corona at various energy levels. Surface-modified PE films were characterized by contact angle measurements and electron spectroscopy for chemical analysis (ESCA). Good wetting was already achieved with treatment at a lower energy level. Various degrees of adhesion were obtained at various degrees of treatment. A hydrophilic monomer, 2-hydroxyethylmethacrylate (HEMA), was polymerized onto the surfaces of polypropylene (PP) with radiation-induced grafting, which was carried out at two different radiation doses. In both cases, a thick, visible layer of polyHEMA was formed on the surface of PP, and satisfactory wetting was already achieved at lower radiation doses. Scanning electron microscopy (SEM) showed that different degrees of roughness were achieved at various radiation doses. Like the case of corona-treated PE, different degrees of adhesion were obtained at different degrees of surface treatment. This study shows that improved wetting alone is not satisfactory for good practical adhesion', regardless of the surface modification method used.     

Structure and properties of rubber-modified polypropylene impact blends

The state of dispersion of poly(ethylene-co-propylene) (PEP) rubber and high-density polyethylene (HDPE) in polypropylene (PP) blends was investigated using scanning electron microscopy to examine solvent-etched microtomed surfaces cut at low temperatures. The validity of the method was established by comparing the areal fraction of dispersed particles in micrographs with the volume fraction of PEP and HDPE in PP-rich blends. When small amounts of PEP and HDPE were added to PP, they combined to form composite PEP–HDPE particles with characteristic internal structures in a PP matrix. Changes in impact strength and flexural modulus with changes in mixing conditions and blend composition were determined and interpreted in terms of the size, composition, and internal structure of the dispersed particles. Particle growth in the melt limited the impact strength level achieved in molded articles. A simple model proposed for screening rubbers for toughening of brittle plastics successfully predicts that PEP rubber should be an excellent impact modifier for PP.     

竹材表面处理对胶合性能的影响

为提高竹材的胶合性能,用自制的偶联剂对竹材表面进行预处理,测试了处理前后表面接触角的变化,从而计算出竹篾外表面自由能及其分量的变化。将处理的竹篾压制成竹篾层积材,测试了竹篾层积材的物理及力学性能,并与未处理竹篾层积材进行了比较。研究结果表明,经偶联剂处理的竹篾表面自由能提高,压制的竹篾层积材的胶合强度也有明显的提高,还对偶联剂处理前后强度变化的原因进行了探讨。     

HEMA接枝CPP的合成及其性能

以甲苯为溶剂,过氧化二苯甲酰(BPO)为引发剂,采用甲基丙烯酸羟乙酯(HEMA)通过自由基聚合接枝氯化聚丙烯(CPP);考察了引发剂类型对接枝反应的影响;研究了反应时间、反应温度、BIN)用量、HEMA用量对接枝率及接枝CPP黏合性能的影响,并对接枝产物进行了傅里叶变换红外光谱分析。确定了较理想的工艺条件：反应温度为110℃．反应时间为5h,m(CPP)／m(HEMA)／m(BPO)为1．0：1．0：0．1。     

氯化聚丙烯改性胶粘剂的合成及粘附性能研究

以甲苯为溶剂,过氧化二苯甲酰(BP0)为引发剂,通过自由基聚合,采用甲基丙烯酸羟乙酯(HEMA)和苯乙烯(St)接枝改性氯化聚丙烯(CPP)。研究了不同苯乙烯用量、不同反应温度、不同反应时间、不同引发剂用量对改性氯化聚丙烯胶粘剂粘附性能的影响,得出较佳的工艺条件为反应温度90℃,反应时问2h,原料配比m(CPP)：m(HEMA)：m(St)：m(BPO)=50：0．5：0．6：0．15。     

Effect of filler content and surface treatment on the tensile properties of glass‐bead‐filled polypropylene composites

The tensile properties of polypropylene (PP) filled with two A‐glass beads with the same size, PP/3000 (glass bead surface pretreated with a silane coupling agent) and PP/3000U (no surface pretreatment), have been measured by using an Instron materials testing machine at room temperature, to identify the effects of the filler surface pretreatment and its content on the tensile properties of these composites. The results show that the Young's modulus E_c of the composites increases non‐linearly with increasing volume fraction of glass beads ϕ_f, while the tensile yield strength σ_yc and tensile stress at break σ_bc of the composites decrease with an increase of ϕ_f, in the ϕ_f range 0–30%. Furthermore, the values of E_c and σ_bc of the PP/3000 system are somewhat higher than those of the PP/3000U system under the same test conditions, but this is in contrast to the tensile strain at break ε_bc and tensile fracture energy E_bc, especially at higher ϕ_f values. Good agreement is shown between the measured tensile strength and the predicted value by using an equation proposed in previous work. In addition, ε_bc and E_bc reach maximum values at ϕ_f = 25% for both systems. This indicates that there is a brittle–ductile transition for the composites in tension. © 2000 Society of Chemical Industry     

聚丙烯催化合金组成与性能研究

利用国产齐格勒-纳塔催化剂在反应器中合成出了聚丙烯（PP）催化合金,并系统地研究了不同气相聚合压力以及气相单体组成比所合成的聚合物合金组成与性能的关系,结果表明,在反应器中直接合成出的PP催化合金具有非常高的常温冲击强度和低温冲击强度,且随着合金中乙丙共聚物含量的增加而增加,但其模量却随之下降;若控制合金中乙丙共聚物的含量不超过10%,则可使PP合金材料既具有较高的冲击强度又具朋较高的模量。     

Plasma-induced hydrogel grafting of vinyl monomers on polypropylene

Polypropylene (PP) film was plasma-treated using a 13.56 MHz direct plasma with argon, nitrogen, and oxygen as the plasma-forming gases. The three gases induced very different changes on the PP film surface, which were studied using contact angle measurements. Because of its degrading and oxidative effect, oxygen plasma pretreatment was not used for the homogeneous grafting of acrylic acid and acrylamide. Nitrogen plasma treatment did not lead to the formation of stable peroxides on the film surface and did not undergo grafting reactions. This may be due to the types of radicals and functional groups created on the surface during the plasma treatment. Finally, argon plasma pretreatment was found to be the most effective for the grafting of vinyl monomers. The amount of grafted poly(acrylic acid) was shown to be proportional to the concentration of peroxides created by argon plasma treatment.     

Forced air plasma treatment for enhanced adhesion of polypropylene and polyethylene

This paper describes our investigation of the effects of forced air plasma treatment on polypropylene and polyethylene. The morphology of the treated surfaces has been carefully examined using a variety of tools including optical profiling. The complex surface morphology was observed to change with increasing treatment and varying intensity of the treatment over the surface. Optimum treatment conditions have been deduced using surface energy determinations and can be compared with the morphological changes. Determinations of surface energy, both the polar and non-polar components, have been made after exposure to varying moisture conditions for varying times. Different results are obtained for different environments and from different materials. These results demonstrate that forced air plasma treatment is a highly effective means of increasing the surface energy of polymers, which can be long-lasting, provided the treated surfaces are kept in dry conditions.     

An investigation on the modification of polypropylene by grafting of maleic anhydride based on the aspect of adhesion

Isotactic polypropylene was modified by a chemical grafting of maleic anhydride in a molten state. The degree of grafting, ranged from 0.078–0.368%, was determined by a titration method. Isotactic polypropylene modified by chemical grafting of maleic anhydride was used as an adhesive in bonding the cold-rolled steel sheets for the correlation of its bondability. It was found that the maximum adhesive strength 159 kg/cm² was obtained from a degree of grafting 0.217%. A higher degree of grafting was detrimental not only to the initial adhesive strength, but also to the durability aged in a wet environment. Electron spectroscopy for chemical analysis was used to analyze the failure loci, because the joint was separated by shearing. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 383–387, 1998     

Surface Characterization of Plasma Treated Carbon Fibers and Adhesion to a Thermoplastic Polymer

The surface chemistry of IM7 carbon fibers was characterized by x-ray photoelectron spectroscopy (XPS). The fiber surface energetics were determined from a two-liquid tensiometric method. The adhesion between as-received and plasma-treated carbon fibers and polyethersulfone (PES) was measured by the microbond pull-out test.

The surface characterization techniques showed that the effect of any plasma treatment is attained within less than 15 seconds. It was found that both argon and air plasmas increased the oxidation state of the fiber surface and that they reduced the dispersive component (γ_s ^d) of the fiber surface free energy considerably. The ammonia plasma treatment resulted in a cleaning of the surface. This plasma treatment was also effective in improving the fiber/matrix adhesion of quenched samples. A similar adhesion enhancement between as-received fibers and PES is obtained by annealing the samples above the Tg of the polymer. The air plasma treatment did not have any significant effect on the fiber/matrix adhesion.     

Influence of ageing on adhesive properties of polypropylene modified by discharge plasma

The adhesive properties of isotactic polypropylene with different degrees of crystallinity, surface‐modified by corona discharge plasma have been studied, during the process of ageing. Considerable decrease in the surface free energy and its polar component was observed. A significant correlation was found between the mechanical work of adhesion to polyvinyl acetate and the polar fraction during ageing. The influence of the crystallinity of the polymer on the resulting adhesion parameters of aged polypropylene foil was confirmed. © 2001 Society of Chemical Industry     

Surface Characterization of Plasma Treated Carbon Fibers and Adhesion to a Thermoplastic Polymer

The surface chemistry of IM7 carbon fibers was characterized by x-ray photoelectron spectroscopy (XPS). The fiber surface energetics were determined from a two-liquid tensiometric method. The adhesion between as-received and plasma-treated carbon fibers and polyethersulfone (PES) was measured by the microbond pull-out test.

The surface characterization techniques showed that the effect of any plasma treatment is attained within less than 15 seconds. It was found that both argon and air plasmas increased the oxidation state of the fiber surface and that they reduced the dispersive component (γ_s^d) of the fiber surface free energy considerably. The ammonia plasma treatment resulted in a cleaning of the surface. This plasma treatment was also effective in improving the fiber/matrix adhesion of quenched samples. A similar adhesion enhancement between as-received fibers and PES is obtained by annealing the samples above the Tg of the polymer. The air plasma treatment did not have any significant effect on the fiber/matrix adhesion.